A third generation mobile communications system is in Europe named UMTS (Universal Mobile Telecommunications System). It is a part of the International Telecommunications Union's IMT-2000 system. UMTS/IMT-2000 is a global wireless multimedia system, which provides higher transmission speed (2 Mbit/s) than the existing mobile networks.
UMTS and the General Packet Radio Service (GPRS) in the Global System for Mobile Communications (GSM) have been developed to provide wireless communications services packet-switched as well as circuit-switched environments.
FIG. 1a shows with a greatly simplified diagram the UMTS network. Only those network elements that are significant in view of the actual invention are shown. Of course, the network may contain one or more of each network element described in the following, depending on the capacity of the element, the number of mobile subscribers, and the organization of the network.
The user terminals 100 may be multi-mode terminals, which can operate using at least two radio access technologies, such as UMTS and GSM, for example.
A Gateway GPRS Support Node (GGSN) 102 is a gateway to external networks, and it acts as a router, routing data packets to and from the GPRS support node currently serving the given GPRS terminal.
A Serving GPRS Support Node (SGSN) 101 is at the same hierarchical level as the mobile switching center MSC. It maintains information about the GPRS terminal's location inside its service area and performs security and user access control functions. During data transfer the serving GPRS support node sends and receives data packets to and from the given terminal via a base station subsystem. The serving GPRS support node requests routing information and subscriber information from the Home Location Register (HLR) 103, where all subscriber information is permanently stored.
A UMTS specification allows a network subscriber to have one or more packet data protocol (PDP) addresses. Each of the addresses is described by one or more packet data protocol contexts in the user terminal, the serving GPRS support node, and the gateway GPRS support node. The packet data protocol context can be selectively and independently activated, modified and deactivated. All packet data protocol contexts of a subscriber are associated with the same Mobility Management (MM) context for the International Mobile Subscriber Identity (IMSI) of that subscriber. When the packet data protocol is set up, this means that a communication channel is set up.
In FIG. 1a the serving GPRS support node and the gateway GPRS support node are located in the same domain A. When a connection is to be set up between a subscriber and the Internet 108, for example, the first step is that a mobile terminal 100 sends an active packet data protocol context request through a radio access network (RAN) 106 to the serving GPRS support node 101. The message includes a variety of parameters, which further include a packet data protocol address and an Access Point Name (APN). The access point name is a logical name referring to the gateway GPRS support node to be used. Here the access point name refers to the gateway GPRS support node 102, through which the data packets are routed between the mobile terminal and the Internet. Several messages are sent between the said network elements before the connection is completed.
Event (Call/session) detailed data collection is always used when specified detailed information on an event (call/session) is required for billing or for the monitoring of event (call/session) details. Thus, each of the network elements collects data pertaining to each call/session until a certain predefined limit has been reached. The limit is a certain amount of data, time or other definable trigger values, such as a megabyte, for example. Then the network element generates an event detail record and sends it using an active protocol through the IP-network (Internet Protocol network) 107 to a Charging Gateway Function CGF1 104. In general, at least the following network elements generate event call detail records: the serving GPRS support node, the gateway GPRS support node, the call state control function (CSCF), and the Application Server(s) in radio access networks, such as a General Packet Radio Service (GERAN) or a UMTS Terrestrial Radio Access Network (UTRAN), the latter being a wideband multiple access radio network currently specified in the 3GPP (Third Generation Partnership Project). Normally, during one session each of the said network elements generates a number of event call detail records relating to the session.
The charging gateway function receives, for example, four event detail records pertaining to the same session from the serving GPRS support node and four from the gateway GPRS support node and then combines them with the help of a sequence number found in each event detail record. A formatted event call detail record is sent from the charging gateway function to a Billing Center (BC) 105 for processing.
A number of problems arise if the method described above is used as such in the latest release of the third generation mobile communications system. Some of the problems are briefly described with reference to FIG. 1b in the following.
Several millions event detail records are constantly generated in each of the network elements, such as the serving GPRS support node 101, the gateway GPRS support node 102, the call state control function CSCF 109, the application server 110, or some other network element N 111. Then each of the network elements independently passes the call detail records to a charging gateway function CGF1-CGFN 112. The problem is that at the moment there is no mechanism which would automatically in real-time centralize directly all the event detail records pertaining to one session for the specified charging gateway function (e.g. CGF1) in the network/domain concerned. By contrast, the event detail records are directed to a large number of different charging gateway functions. This leads to the problem of how to combine those event detail records pertaining to the same session/call. One solution is to use a standalone device, a so-called mediator, for collecting and combining the event detail records before sending them for further processing to the billing center 106. Combining the event detail records in the mediator is quite complicated and time-consuming.
One solution is to use a unique session identifier for combining the right event detail records. This kind of solution is described in the applicant's earlier U.S. patent application Ser. No. 09/577,152, which has not been published by the filing date of the present application. The identifier is called a global transaction ID (unique session identifier.)
However, that solution does not solve the time-consuming problem above, i.e. different network elements still send event detail records to different charging gateway functions.